var verify_retail_tax_comment = JSON.parse('{"CODE":0, "ACTION":"","LEVEL":"T1", "MSG":"","DATA":"","SCRIPTNAME":"verify_retail_tax_comment"}');

if (!isNull(retail_tax) && isNull(retail_comment)) {
    verify_retail_tax_comment.CODE = 2;
    verify_retail_tax_comment.ACTION = 'error';
    verify_retail_tax_comment.MSG = '有更新零售，变价原因不能为空';

}

JSON.stringify(verify_retail_tax_comment);